This application is based on Patent Application No. 2001-284037 filed Sep. 18, 2001 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink jet printing apparatus for printing an image by ejecting ink stored in an ink tank from a print head and to ink ejection performance recovery device and method for the ink jet printing apparatus. More specifically, the present invention relates to an improvement in a recovery operation performed to keep an ink ejection of the print head in an appropriate condition.
2. Description of the Related Art
In recent years, printers, facsimiles and copying machines using an ink jet printing system are rapidly expanding into the market.
Ink jet printing apparatus in general use have a print head for ejecting ink droplets and an ink tank for supplying ink to the print head. In one type of these ink jet printing apparatus which has a print head and an ink tank formed integral as one piece, when the ink tank runs out of ink, the print head as well as the ink tank must be replaced, increasing a consumption of consumable parts and therefore a running cost.
To deal with this problem, it is currently practiced to separately form a print head and an ink tank, removably assemble them together and mount them on a carriage. In this case, when the ink tank runs out of ink, only the ink tank needs to be replaced, significantly reducing the running cost when compared with the type in which they are formed integral as one piece. In the above construction having an integrally formed ink tank and print head, in further reducing the running cost it is effective to increase the capacity of the ink tank. Particularly, in a printer that prints a large number of sheets, such as a network printer in office, a problem may arise that unless a capacity of the ink tank or the number of sheets that can be printed with one ink tank is set large, a frequency at which the ink tank needs to be replaced will increase. It is therefore necessary to use a large capacity ink tank to reduce a burden of replacement work on the part of the user.
As the capacity of the ink tank increases, however, the carriage holding the print head and the ink tank also increases in size and weight. As the weights of the carriage and the ink tank increase, it becomes difficult to scan the carriage at high speed, rendering a high-speed printing difficult to achieve. Of course, the high-speed printing may be realized by using a high torque motor for driving the carriage but with an increased cost of the motor.
To cope with this problem, a printing apparatus has been put into practical use, in which only the print head is mounted in a carriage, with the ink tank fixed at a predetermined position on other than the carriage in the ink jet printing apparatus and connected to the print head as by a tube. In this apparatus, since what is mounted on the carriage is only a light-weight print head, the scanning of the carriage can be done at high speed without requiring a large motor. The capacity of the ink tank fixedly installed on other than the carriage can be selected appropriately by considering the running cost, the size of the apparatus and the frequency of ink tank replacement.
FIG. 10 is a conceptual diagram showing a printing apparatus having a print head and an ink tank connected through a tube.
Denoted 1 is a print head mounted on a carriage (not shown), 2 an ink tank, 3 a supply tube connecting the print head to the ink tank 2, and 4 an atmosphere-communication tube connected to the ink tank 2. When the print head 1 performs printing, ink in the ink tank 2 is supplied through the supply tube 3 to the print head 1. The same volume of air as the ink supplied to the print head 1 is introduced into the ink tank 2.
In the construction shown in FIG. 10, the ink tank mounted in the carriage is ideally replaced with a new one when the ink in the ink tank is completely used up. Replacing the ink tank at such a timing can be said to be ideal from the standpoint of an ink use efficiency in ensuring that the ink in the ink tank is completely consumed, and also from the standpoint of an ejection function in ensuring that air is not trapped into the tube by stopping the ink use just before the ink in the tube begins to be used. When air is trapped in the tube, the air will be taken into the print head as the print head continues printing, resulting in a failure to eject ink properly. It is therefore necessary to avoid the air being trapped into the tube.
Assuming that air may get trapped in the tube, it is possible to perform the recovery operation every time the ink tank is replaced In that case, there is a high possibility of unnecessary or redundant recovery operations being carried out, thus wasting the ink and time. During the recovery operation all the ink in the tube and the print head needs to be sucked out and removed, and thus a large volume of ink is consumed. When the above-described excess recovery operation is executed, a large amount of ink is wasted, increasing the running cost. Further, if the amount of ink discharged increases, a waste ink absorbing unit in the printing apparatus needs to be increased in capacity, which in turn leads to an unwanted increase in the overall size of the printing apparatus.
As described above, preventing air from being rapped in the tube is desirable also to make the recovery operation unnecessary after the replacement of the tank. For this purpose, detection means for detecting the amount of ink remaining in the ink tank needs to be provided.
Generally known residual ink volume detection means currently available include a discharge volume detection system that detects an ink discharge volume by counting the number of ink droplets ejected from a print head or metering an ink volume sucked out by recovery means, and a system that detects a residual ink volume by measuring a voltage change when a predetermined current is applied to a pair of electrodes installed in a tank.
Although the ink in the ink tank should be used up completely as described above, because it is impossible to determine what kind of image the user will print, it is necessary to stop using the ink tank just before the ink is consumed completely to allow a certain amount of ink to remain in the tank.
FIG. 11 shows a level of ink when the tank use is finished. For example, the residual ink volume detection means detects when the ink level reaches a position indicated by an arrow A in the figure, and decides that the ink tank has reached its final stage of use. At this time, the ink tank must contain a volume of ink that will allow a solid print image with a maximum print duty of 100% to be printed on a print medium of the largest size that can be used on the printing apparatus. If this volume of ink is not left in the tank, the ink in the tube may be consumed, causing air to enter into the tube.
When the final stage of tank use as indicated by the arrow A is reached, the ink tank must be replaced despite the fact that the tank still contains a certain volume of ink with which a low-duty printing can be performed. This is therefore not desirable from the standpoint of an ink use efficiency.
This is explained in more detail. In a printing operation that prints on, a print medium at a resolution or density of 600 pixels per inch with 30 picoliter of ink ejected to each pixel, for example, the amount of ink required to form a solid image of 100% print duty on a A3-size print medium is approximately 2 cc. Suppose that the amount of ink remaining in the tank when the residual ink level reaches the position of arrow A in FIG. 11 is 1 cc. In this condition, performing the above printing operation immediately before the ink level of arrow A is reached will cause the ink in the tube to be consumed and air to get into the tube. Thus, if a setting is made so that about 2 cc of ink remains when the ink level is at the arrow A position, i.e., at the final stage of tank use, the above problem is eliminated but the 2 cc of ink is wasted. This volume of ink wasted corresponds to 40 sheets of A4-size paper printed at a 5% duty.
Next, a recovery operation will be explained. The recovery operation involves operating a pump connected to a cap member adapted to engage the print head and generating a negative pressure in the cap to suck out ink from the print head. The amount of ink consumed by the recovery operation (discharge volume) can be set at an appropriate value according to a purpose of the recovery operation performed. For example, when several nozzles fail to eject ink or a printed image has light or dark strips or density variations, a recovery operation with a comparatively small ink consumption is executed. When air accumulated in the print head or tube is removed or when the printing apparatus has not been used for several weeks or months, a recovery operation with a comparatively large ink consumption is carried out. It is assumed here that the ink consumption by the latter recovery operation is 5 cc.
The final-stage-of-use position indicated by arrow A of FIG. 11 must be set so that the ink in the tube will not be consumed whichever recovery operation is executed. That is, the residual ink volume A needs to be set to 5 cc to accommodate a worst case in which a recovery operation with the largest ink consumption may be performed immediately before the arrow A position is reached. With this setting it is possible to reliably prevent the ink in the tube from being consumed by the recovery operation. However, when the residual ink volume reaches 5 cc after the normal printing operation, it is decided that the final stage of tank use is reached and thus the ink tank must be replaced. The 5 cc of residual ink is even larger than the residual ink volume set in the preceding case that allows the A3-size medium printing.
An object of the present invention is to provide an ink jet printing apparatus capable of using as much ink in an ink tank as possible and minimizing a residual ink volume at time of tank replacement.
According to a first aspect, the present invention provides an ink jet printing apparatus for performing a printing with a print head which ejects ink supplied from an ink tank, in the form of droplets, the printing apparatus comprising: a print head for ejecting ink droplets; an ink tank for storing ink to be supplied to the print head; recovery means for keeping an ejection performance of the print head in appropriate condition by discharging ink from the print head; a residual ink volume detection means for detecting a residual ink volume in the ink tank; and a discharge ink volume control means for controlling a discharge ink volume to be discharged by the recovery means when the residual ink volume detected by the residual ink volume detection means is less than or equal to a predetermined value.
In the above aspect, the ink tank may be connected to the print head through a predetermined ink supply path.
Further, the discharge ink volume control means may set two or more discharge ink volumes to be discharged by the recovery means.
Further, the recovery means may be able to perform a plurality of recovery operations with different discharge volumes and the control means may select one of the recovery operations according to the residual ink volume in the ink tank.
Further, the recovery means may include a cap that hermetically contacts an ink nozzle surface of the print head and pressure generation means connected to the cap, and a negative pressure generated by the pressure generation means may be applied to an interior of the cap in hermetic contact with the ink nozzle surface of the print head to discharge ink from the nozzles.
Further, the residual ink volume detection means may comprise metering means for measuring an ink volume flowing out of the print head and calculation means for determining the residual ink volume by subtracting the ink volume measured by the metering means from a maximum storage volume of the ink tank.
Further, the residual ink volume detection means may comprise a pair of electrodes provided on a bottom of the ink tank, an annular wall enclosing at least one of the electrodes, a constant current source for applying a constant current between the electrodes through the ink and a voltage detection means for detecting a voltage between the electrodes, and detect the residual ink volume from the voltage detected by the voltage detection means.
According to another aspect, the present invention provides a recovery device in an ink jet printing apparatus, wherein the ink jet printing apparatus has a print head for ejecting ink droplets and an ink tank for storing ink to be supplied to the print head, the recovery device comprising: recovery means for keeping an ejection performance of the print head in appropriate condition by discharging ink from the print head; a residual ink volume detection means for detecting a residual ink volume in the ink tank; and a discharge ink volume control means for controlling a discharge ink volume to be discharged by the recovery means when the residual ink volume detected by the residual ink volume detection means is less than or equal to a predetermined value.
According to still another aspect, the present invention provides a recovery method used in an ink jet printing apparatus for keeping an ejection performance of a print head in appropriate condition by performing a recovery operation of discharging ink from the print head, wherein the ink jet printing apparatus has the print head for ejecting ink droplets and an ink tank for storing ink to be supplied to the print head, the recovery method comprising the steps of: detecting a residual ink volume in the ink tank; and controlling a discharge ink volume to be discharged by the recovery operation when the residual ink volume detected by the residual ink volume detection step is less than or equal to a predetermined value.
In the invention having the construction described above, since the ink consumption by the recovery operation is limited according to the residual ink volume in the ink tank, the residual ink volume at the end of use of the ink tank can be reduced significantly, thus making an efficient use of the ink.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.